Combined detector amplifier circuits



April 9, 1935. V DER VEN ET AL 1,997,397

. COMBINED DETECTOR AMPLIFIER CIRCUITS Filed Dec. 8, 1933 INVENTORS A0/F/AA US J./7. I/A/V 05/? 14w JAM M44 01-7? win/r BHPIVARQUS 0.19.

BY g M5654" ATTORNEY inserted in this rectifier circuit, C2 the coupling Patented Apr. 9, 1935 l Q, ooinsmnnenniraoron AMPLIr ine Q:

- omomrs I Mamas ohar'r'nes dei Malr lt, ana nsnmaus Dorninicusli'nbertus 1 t 1 '1'1611826'11', Eindhoven,Netherlands assigfiors1o Radio Gorpcratiohimf America, a corporation:

This invention relatesto a coupling arrangement for rectifying high frequency oscillations with subsequent amplification and more particular ly'to a combined detector arfipli ffer arrange merit. The inven tic inisparti "'6 this condenser beingiconnected, without the in terposition of high frequency resistances; to the electrode of the rectifier hayin'grfa con'stant poten'tial sand the other lp'ole being connected to the controlling'grid of the amplifier.

tions are set up at the grid of the amplifier placed behind a detector, since these oscillations may cause a small stability of the arrangement. This. drawback manifests itself more particularly with superheterodyne receivers. By using the above;

arrangement one obtains already that extremely small tensions are set up at the controlling grid. In spite thereof, part of the high-frequency voltages impressed on the detector will still be present in the input circuit of the low frequency amplifier, because the said condenser, which offers substantially no resistance to high frequency currents, together with the capacity of the diode forms a potentiometer over the input circuit of the detector. The part of the high frequency voltages thus set up at the condenser, is supplied to the grid .of the amplifying tube.

The present invention provides means for avoiding that high frequency voltages are set up at the grid of the amplifier placed behind This is achieved by inserting in' the detector. the arrangement set out a capacity. between the grid of the amplifying tube and the electrode of the rectifier which electrode has no constant potential, said capacity having such a size that the capacities C1, C2, C3 and Cr form a balanced bridge, C1 denoting the capacity of the condenser capacity through which this condenser is connected to the controlling grid of the amplifying tube, C3 the capacity'placed between the grid of the amplifying tube and the electrode of the rectifier which has no constant potential, and C4 designating the capacity of the rectifier.

The invention will be more clearly understood by reference to the accompanying drawing representing, by way of example, one form of construction thereof.

In the drawing I denotes a united detector and amplifying tube comprising a cathode 2. This r s, 1933,, Serial no, 701.47 f l il Germany DecemBerZ, 1-932= (01. 250-27) cathode "which, may be constructed as an equipotentialrcathode, is rcommon 'to the rectifier and thetamplifier, 'B'y Bis designated the anode of the rectifier and =by 41.13118 controlling: grid, of {the amplifier whichjm'ay comprise,.moreover, a pro:

tectinggridfdiand ananode 6. In the input circuit offzth-e :rectifieris inserteda tuned. circuit --'l-.2which is connected on one hand directly to :the anode :3 of the rectifier andon the otherlhand' through a condenser 8 and a leakage. resistance astoythe cathodeof the rectifier. I

,1 The sand of the :condenser 8 which is-not 'connected to the cathode is. connected to the 'oontrolling grid of the amplifying tube through a It is imperative that no high frequency oscillacondenser ID. A negative grid voltage canbe supplied to the controlling grid of the amplify ing tube through the resistance l I which is connected to a point having a negative potential with respect to the cathode. The capacity of the rectifier may be denoted by the condenser l2 which is indicated in dotted lines on the drawing.

According to the invention a condenser 13 is inl ma 6 i serted between the anode 3 of the rectifier and V the grid 4 of the amplifier which condenser has such a size that the total capacity inserted between this anode and said grid has a value C2 denoting the capacity of the condenser 10, C1 the capacity of the condenser 8 and C4 designating the capacity of the condenser l2.

Preferably the tube used in this arrangement is equippedwith an equi-potential cathode which slightly projects from the electrode system of the amplifier'and is surrounded at this point with a small auxiliary anode which serves as anode of the rectifier system. In a suitable form of construction of such a system the capacityCr has circuit arrangement for the diode rectifier com prising a connection between the rectifier cold electrode and the cathode, said connection ineluding means for impressing high frequency signal currents on said circuit and a first condenser in series, a resistor shunted across said first condenser, an amplifier input circuit for said tube comprising a connection from a second cold electrode thereof to the cathode, said connection including a second condenser in series with the arrangement comprising the first condenser and shunted resistor'whe'reby the rectified voltage developed in the diode circuit is impressed upon: the amplifier input circuit, means including a third condenser'for connecting the second cold" electrode to the first cold electrode, an'amplifier output circuit for said tube comprising a connec-' tion including a source of current between a third cold electrode of the tube and the cathode thereof, there being inherent capacity between the first named cold electrode and the cathode, said third condenser being proportioned'so that the total capacity inserted between the first cold. electrode and the second cold electrode has approximately the value C2 X C4 Where C2 denotes the capacity of the second condenser, C1'the capacity of the first named.con-' denser and C4 the inherentcapacity between the first named cold electrodeland the cathode.

-2. In a combined detector amplifier, an electronic tube provided with a cathode and a plurality of cold electrodes, said tube having its cathode and one of its cold electrodes disposed to serve as a'diode and the cathode and the other a r cold electrodes arranged so as to serve: as an uamplifier, external circuits for forming adiode rectifier circuit and an amplifier circuit, the'diode circuit comprising a connection including a first condenser between the diode cold electrode and the cathode, the amplifier being provided with an input circuit and an output circuit, said input circuit comprising a connection including a second condenser andthe first condenser in series between a second cold electrode and the cathode,

, means for impressing a carrier wave signal upon said diode circuit, means for impressing the recti- -fied voltage developed in the diode circuit upon balanced bridge circuit, the thirdicondenser hav ing a capacity value such that the total capacity between the diode coldelectrode and the second cold electrode is approximately equal to V r C1 7 I where C denotes the capacity, of the second con- "densen'C the-capacity of the first condenser and ADRIANUS JOI-IANNES b HEINS VAN DER VEN.

JAN VAN DER MARK. r

'BERNARDUS DOMINICUS HUBERTUS TELLEGEN. 

